In vitro drought tolerance in selected elite clones of Eucalyptus tereticornis Sm.

The selected elite clones of Eucalyptus tereticornis were screened for drought tolerance on Murashige and Skoog (MS) medium containing 2.5 mu M benzyl adenine, 0.5 mu M alpha-naphthaleneacetic acid and different concentrations of d-mannitol (0, 250, 500, 750, and 1000 mM). All the clones recorded a significant reduction in culture growth index (CGI) with an increase in d-mannitol concentration, this reduction was minimum in case of clone 'KE8' with maximum CGI (247.89%) and minimum CGI (141.12%) on medium containing 250 mM and 1000 mM d-mannitol, respectively. Higher chlorophyll content (156.5 mu g g(-1) FW) was recorded in clone 'KE8' on medium containing 250 mM d-mannitol, and significantly lower levels were observed in other clones with the increase in d-mannitol concentration. Relative water content (RWC) also decreased significantly with maximum reduction in clone 'Y8' and minimum in case of clone 'KE8'. Higher levels of proline and sugar accumulation were recorded in the cultures of clone 'KE8' on medium containing 1000 mM d-mannitol. Maximum activity of superoxide dismutase (SOD) (11.08 U mg(-1) protein) was also recorded in the cultures of clone 'KE8' on exposure to water stress, while the cultures of clone 'Y8' recorded minimum SOD activity under similar condition. Similar trends for the activity of other antioxidant enzymes such as catalase, peroxidase, and ascorbate peroxidase were also observed.